Clarify how to use a negated expression in an if statement

[albbus-stack]

Why:

Makes a clearer explanation of a negated expression inside an if statement.

Closes: #28308

What's being changed (if available, include any code snippets, screenshots, or gifs):

All the changes are as requested by @hubwriter in this comment.

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• I have reviewed my changes in staging, available via the View deployment link in this PR's timeline.

  • For content changes, you will also see an automatically generated comment with links directly to pages you've modified. The comment won't appear if your PR only edits files in the data directory.

• For content changes, I have completed the self-review checklist.

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The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

You may find it useful to copy this table into the pull request summary. There you can edit it to share links to important articles or changes and to give a high-level overview of how the changes in your pull request support the overall goals of the pull request.

Source	Preview	Production	What Changed
actions/learn-github-actions/expressions.md	fpt ghec ghes@ 3.10 3.9 3.8 3.7 3.6 ghae	fpt ghec ghes@ 3.10 3.9 3.8 3.7 3.6 ghae

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fpt: Free, Pro, Team
ghec: GitHub Enterprise Cloud
ghes: GitHub Enterprise Server
ghae: GitHub AE

[cmwilson21]

@albbus-stack Thanks so much for submitting a PR! I'll get this triaged for review ⚡

[albbus-stack]

@albbus-stack Thanks so much for submitting a PR! I'll get this triaged for review ⚡

The code block in data/reusables/actions/expression-syntax-if.md fails the content-linter action with:

Error name:    "ParseError"
Error message: "unexpected token at \"! startsWith(...\", line:6, col:6"

Both /actions/using-workflows/workflow-syntax-for-github-actions and /actions/creating-actions/metadata-syntax-for-github-actions break in the preview because they have that reusable.

[SiaraMist]

Thank you so much for picking up this issue and making these changes, @albbus-stack! I made a couple of edits just to formatting that got all of the tests passing, so I'll go ahead and get this merged. Thank you again for contributing to the docs! 🚀

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